I wouldn't go lower then a 27" neck if I could help it, the only seven string like that is going to be expensive. I think the guy from deftones has a signature like that with some company but they are expensive. Ibanez used to make them but they stopped so good luck finding one. Schecter makes a 26.5" one which probably is your best bet but it isn't ideal.

Also you may have to swap out the tuners, nut, and possibly bridge (most likely not the bridge if it is fixed) to get the heavy string gauge to work. That and adjust the the guitar for it too truss rod, innotation... the standard...

It might be hard but I think it is worth it... although you could just opt for an 8 string and forgo all of that work...

Good luck mate, and yes you do really need to go that low , except I would change that high F# to a G... but that is just me...